Glass Knifefish

Geographic Origin and Biotope: Amazon and Orinoco River basins, in South America. Lives among the roots of flooded forests and dense patches of submerged vegetation in murky waters.

Taxonomy and Morphology: Glass Knifefish / Green Knifefish (Eigenmannia virescens). Neotropical "knife" fish. Transparent/diaphanous and lacking dorsal and caudal fins, it swims exploiting the undulations of the very long anal fin in an almost hypnotic motion (backwards and forwards in the same way).

Social Behavior: Crepuscular and nocturnal. Extremely gregarious: lives in schools, using weak bio-electric fields (electrogenesis) to communicate and orient itself (EOD). Isolated, it wastes away.

Coloration and Sexual Dimorphism: Translucent/glassy body with greenish reflections. The internal organs can be glimpsed. Males usually have stronger EODs and larger sizes, but are indistinguishable by sight.

Aquarium Setup: Long tank (at least 120-150 cm / 48-60 inches). Decor: "Chaos". Woods of tangled timber, PVC pipes or thick bushes of plants, dim lighting. Requires space so as not to electrically trip over conspecifics, even while crowding together by day.

Diet and Feeding: Insectivore and carnivore. Must be fed strictly with the lights out. Prefers bloodworms, tubifex (washed) and small live/frozen invertebrates. Will ignore pellets and flakes for a long time.

Water Quality: Seeks clean and well-filtered water; powerful filtration must not, however, translate into a "torrent" style water jet. Oversized biological filtration is preferable (peat waters).

Compatibility and Tankmates: Ideal with peaceful South American fish that sleep at night, such as large schools of Tetras and Corydoras, provided they are not so small as to fit in its mouth. No aggressive cichlids (Astronotus).

Aquarium Reproduction: Very rare in captivity, it is induced by the simulation of the rainy season (temperature drops, spray rain and great availability of live food). The eggs are laid in the fronds (mosses).

Risks and Diseases: Fish lacking classic scales, it is Hypersensitive to chemical cures, copper and malachite green (halved doses mandatory). Do not cut or entangle the long "tail" which acts as a sensory radar.